Large tracts of public and private lands are kept mowed during the growing season for aesthetic and safety reasons. The shoulders and median strips of most highways are kept mowed for visibility and appearance reasons. The lawns found in public parks, private estates and institutional grounds are also mowed to maintain an attractive appearance and to reduce insect populations such as jiggers and mosquitoes. Reciprocating blade mowers, such as those used for harvesting crops, are sometimes used to trim turf grass, yet these devices can be hazardous due to their exposed cutting blades. For very fine cutting, such as on golf greens and bent grass turfs, mowers employing gangs of cutting cylinders are sometimes employed, but proper use is time-consuming, and the mowers themselves are subject to jamming and higher maintenance.
Perhaps the most widely used type of mower, both for landscape and roadside mowing, is the rotary blade mower. Where wide areas must be mowed, three or more rotary blade are often used. Belt and pulley blade drive systems can require high maintenance, and safety requires that multiple guards be installed and adjusted. A preferable mower blade rotation system uses hydraulic motors directly mounted to the mower blade spindle to directly drive the rotary blade or blades. The use of hydraulic motors in combination with bearings which are lubricated with hydraulic fluid has proven effective. If the bearings are of the type which does not use ball bearings, the rotors can better withstand the blade striking a solid object such as a rock or sprinkler head.
Various organizations have promulgated standards for rotary mower safety which require the mower blade to be able to survive a sudden stop when a steel rod is suddenly placed in the path of the blade near the blade tip. These "stake tests" are designed to simulate the mower blade striking a solid object, and the ability of a mower spindle to withstand such a test is indicative of mower safety and durability. Mower reliability is enhanced by increasing the amount of lubricating fluid which passes through the bearings. Hydraulic motors operate on high pressure hydraulic fluid which, if not properly drained from the bearings, can develop high pressures in the bearings which will blow the shaft seal.
What is needed is an improved hydraulic motor and mower blade spindle which has good bearing lubrication and which prevents pressure buildup behind the spindle shaft seal.